Biomechanical aspects of the posteromedial split in bicondylar tibial plateau fractures-a finite-element investigation.

PURPOSE: To gain principal insight into fixation techniques of a posteromedial split fragment in bicondylar tibial plateau fractures. METHODS: A computer simulation was performed, applying the finite-element method (FEM) to compare four methods of fixation of the posteromedial split fragment: lateral plate (model 1), lateral plate and kickstand screw (model 2), lateral plate and two antero-posterior lag screws (model 3), and lateral and posteromedial plate (model 4). The displacement of the fragment and material stresses in implants and bone under 2500 N axial load were analyzed. RESULTS: Maximal displacement of the posteromedial split fragment of 2.8 mm was found with a sole lateral plate. An added kickstand screw decreased the displacement to 1.46 mm. Added lag screws improved stability by a factor 4, with a maximal displacement of 0.76 mm. The double-plate configuration revealed 0.27 mm, a decrease of the displacement by a factor 10 compared to model 1. An additional analysis of posteromedial fragment displacements with osteoporotic bone, simulated by dividing the elastic modulus of the bone by a factor 2, turned out to be of relevant impact. For model 1, the calculations did not converge. The influence of bone quality was found to be 70% in model 2, 60% in model 3, and 40% in model 4. CONCLUSIONS: The results indicate that the additional fixation of a posteromedial split fracture by plate osteosynthesis might be advantageous in bicondylar tibial plateau fractures treated with lateral plating. This might be even more important in patients with low bone quality.

An electronically instrumented internal fixator for the assessment of bone healing.

OBJECTIVES: The monitoring of fracture healing is a complex process. Typically, successive radiographs are performed and an emerging calcification of the fracture area is evaluated. The aim of this study was to investigate whether different bone healing patterns can be distinguished using a telemetric instrumented femoral internal plate fixator. MATERIALS AND METHODS: An electronic telemetric system was developed to assess bone healing mechanically. The system consists of a telemetry module which is applied to an internal locking plate fixator, an external reader device, a sensor for measuring externally applied load and a laptop computer with processing software. By correlation between externally applied load and load measured in the implant, the elasticity of the osteosynthesis is calculated. The elasticity decreases with ongoing consolidation of a fracture or nonunion and is an appropriate parameter for the course of bone healing. At our centre, clinical application has been performed in 56 patients suffering nonunion or fracture of the femur. RESULTS: A total of 39 cases of clinical application were reviewed for this study. In total, four different types of healing curves were observed: fast healing; slow healing; plateau followed by healing; and non-healing. CONCLUSION: The electronically instrumented internal fixator proved to be valuable for the assessment of bone healing in difficult healing situations. Cost-effective manufacturing is possible because the used electronic components are derived from large-scale production. The incorporation of microelectronics into orthopaedic implants will be an important innovation in future clinical care.Cite this article: B. Kienast, B. Kowald, K. Seide, M. Aljudaibi, M. Faschingbauer, C. Juergens, J. Gille. An electronically instrumented internal fixator for the assessment of bone healing. Bone Joint Res 2016;5:191-197. DOI: 10.1302/2046-3758.55.2000611.

[Medical Emergency Preparedness in offshore wind farms : New challenges in the german north and baltic seas]. / Notfallmedizinische Versorgung in Offshore-Windparks : Neue Herausforderungen in der deutschen Nord- und Ostsee.

BACKGROUND: Offshore windfarms are constructed in the German North and Baltic Seas. The off-coast remoteness of the windfarms, particular environmental conditions, limitations in offshore structure access, working in heights and depths, and the vast extent of the offshore windfarms cause significant challenges for offshore rescue. Emergency response systems comparable to onshore procedures are not fully established yet. Further, rescue from offshore windfarms is not part of the duty of the German Maritime Search and Rescue Organization or SAR-Services due to statute and mandate reasons. Scientific recommendations or guidelines for rescue from offshore windfarms are not available yet. The present article reflects the current state of medical care and rescue from German offshore windfarms and related questions. The extended therapy-free interval until arrival of the rescue helicopter requires advanced first-aid measures as well as improved first-aider qualification. Rescue helicopters need to be equipped with a winch system in order to dispose rescue personnel on the wind turbines, and to hoist-up patients. For redundancy reasons and for conducting rendezvous procedures, adequate sea-bound rescue units need to be provided. In the light of experiences from the offshore oil and gas industry and first offshore wind analyses, the availability of professional medical personnel in offshore windfarms seems advisible. Operational air medical rescue services and specific offshore emergency reaction teams have established a powerful rescue chain. Besides the present development of medical standards, more studies are necessary in order to place the rescue chain on a long-term, evidence-based groundwork. A central medical offshore registry may help to make a significant contribution at this point.

Biomechanical methods for the assessment of fracture repair.

The progress of fracture healing is directly related to an increasing stiffness and strength of the healing fracture. Similarly the weight bearing capacity of a bone directly relates to the mechanical stability of the fracture. Therefore, assessing the progress of fracture repair can be based on the measurement of the mechanical stability of the healing fracture. However, fracture stability is difficult to assess directly due to various obstacles of which shielding of the mechanical properties by the fracture fixation construct is the most relevant one. Several assessment methods have been proposed to overcome these obstacles and to obtain some sort of mechanical surrogate describing the stability of the fracture. The most direct method is the measurement of the flexibility of a fracture under a given external load, which comprises the challenge of accurately measuring the deformation of the bone. Alternative approaches include the measurement of load share between implant and bone by internal or by external sensors. A direct 3 dimensional measurement of bone displacement is provided by radiostereometric analysis which can assess fracture migration and can detect fracture movement under load. More indirect mechanical methods induce cyclic perturbations within the bone and measure the response as a function of healing time. At lower frequencies the perturbations are induced in the form of vibration and at higher frequencies in the form of ultrasonic waves. Both methods provide surrogates for the mechanical properties at the fracture site. Although biomechanical properties of a healing fracture provide a direct and clinically relevant measure for fracture healing, their application will in the near future be limited to clinical studies or research settings.

Telemetric assessment of bone healing with an instrumented internal fixator: a preliminary study.

In an interdisciplinary project involving electronic engineers and clinicians, a telemetric system was developed to measure the bending load in a titanium internal femoral fixator. As this was a new device, the main question posed was: what clinically relevant information could be drawn from its application? As a first clinical investigation, 27 patients (24 men, three women) with a mean age of 38.4 years (19 to 66) with femoral nonunions were treated using the system. The mean duration of the nonunion was 15.4 months (5 to 69). The elasticity of the plate-callus system was measured telemetrically until union. Conventional radiographs and a CT scan at 12 weeks were performed routinely, and healing was staged according to the CT scans. All nonunions healed at a mean of 21.5 weeks (13 to 37). Well before any radiological signs of healing could be detected, a substantial decrease in elasticity was recorded. The relative elasticity decreased to 50% at a mean of 7.8 weeks (3.5 to 13) and to 10% at a mean of 19.3 weeks (4.5 to 37). At 12 weeks the mean relative elasticity was 28.1% (0% to 56%). The relative elasticity was significantly different between the different healing stages as determined by the CT scans. Incorporating load measuring electronics into implants is a promising option for the assessment of bone healing. Future application might lead to a reduction in the need for exposure to ionising radiation to monitor fracture healing.

Subjective evaluation of a novel method of dose reduction by optical re-exposure of conventional radiographs - a multi-observer region of interest evaluation in an animal model.

A procedure previously been described that has an effect on the image quality and radiation dose of conventional radiographs already at the time of acquisition [Paech A, Schulz AP, Hahlbrauck B, Kiene J, Wenzl ME, Jürgens C. Physical evaluation of a new technique for X-ray dose reduction: measurement of signal-to-noise ratio and modulation transfer function in an animal model. Physica Medica 23 (2007):33-40]. This development is using X-ray sensitization by optical re-exposure. Aim of this study was to establish if the results of optical re-exposure measured with SNR and MTF also meant that the subjective quality of 50% dose-reduced and re-exposed radiographs of bony structures was equal or better than conventional full dose radiographs of the same area. Freshly slaughtered anterior shoulders of lambs served as the animal model. A comminuted fracture in the middle of the shaft was artificially produced. After taking a normal exposed reference image, dose-reduced, five underexposed images were prepared. These underexposed X-rays were then optically re-exposed for a defined period of time before development. The subjective changes in the image quality (information loss or gain) of the images were compared to the reference image and evaluated by 16 physicians with large experience in diagnosis of orthopedic radiographs. The evaluation of the observers scoring showed a significant decrease in the subjective image quality regarding the detail recognition in all images apart from the images re-exposed for 60s. In conclusion, there is a possibility of reducing the collective radiation dose whilst keeping a high degree of diagnostic reliability. Film sensitization provides a technically simple and inexpensive procedure, which can be easily integrated into common film development processes and could considerably reduce patient radiation exposure as well as improve image quality and thus detail recognition.

Locked vs. unlocked plate osteosynthesis of the proximal humerus - a biomechanical study.

BACKGROUND: Locked plates (internal fixators) have been found to be an optimal method for the fixation in proximal humeral fractures. In a biomechanical cadaver study the difference between locked and non-locked osteosyntheses was investigated. METHODS: Paired humeri were harvested, bone density measured. Locked internal fixators were mounted on one specimen; identical plate-screw-systems without locking mechanism applied to the contralateral specimen for comparison. After that, a transverse subcapital osteotomy was performed. With 7 pairs of humeri static tests with increasing axial loads and with 5 pairs dynamic tests with 10 N preload and 80 N maximal axial load for up to 1 million cycles were performed. RESULTS: In the static experiments the elastic stiffness of the construct was 74% higher in the locked group (median 80 N/mm, quartile range 77-86 N/mm) compared with the non-locked group (46 N/mm, 35.5-56.5 N/mm). The difference was statistically significant (Wilcoxon test for paired samples, P<0.05). Similarly, the linear range until failure was definitely extended in the locked group by 64% (92 N, 89-98 N vs. 56 N, 36.5-73.5 N, P<0.05). Under dynamic loading the non-locked group showed fixation failures between 97,000 and 500,000 cycles. In the locked group no failure was observed until the end of the experiment at 1 million cycles (P<0.0.5). The final deformation was found to be 1 mm (median, quartil range 1.0-1.2 mm) in the non-locked group and 0.3 mm (0.2-0.3 mm) in the locked group (P<0.05). The differences were found equally in lower as well as in higher bone density specimen. INTERPRETATION: Because of the optimal load transfer between implant and cancellous bone, a locked screw plate interface will reduce fixation failure in proximal humeral fractures.

[Fracture of the distal lower limb: two-stage surgical treatment with external fixator and locked-screw plate]. / Distale Unterschenkelfraktur: Zweizeitiges Vorgehen mit Fixateur externe und winkelstabiler Platte.

From January 1999 until October 2004 we treated 42 patients with closed fractures of the distal calf by a two-stage treatment plan: first the fracture was stabilized with an external fixator bridging the ankle joint. Second, after an average period of 8.3 days, an open reduction and internal fixation with a locked-screw implant followed. As complications we saw a superficial wound necrosis in 3 cases, 2 patients needed an early bone graft after insufficient bone healing and in one case a deep vein thrombosis of the thigh occurred. A deep infection or osteitis were not seen. 17 patients showed no deficit in the range of movement of the ankle joint compared to their opposite side, 21 patients had a deficit of movement of one third compared to the opposite side and 4 patients suffered from a deficit of (2/3). Radiologically we saw in 31 fractures of the pilon-tibiale in 19 cases no or only few arthrosis of the ankle joint, in 9 cases intermediate and in 3 cases advanced arthrosis. With a two-stage surgical treatment with external fixator and locked-screw implant we achieved a good functional result with only few complications.

Quadriceps tendon ruptures-is there a complete functional restitution?

From January 1986 to November 1999, 35 patients with 36 traumatic ruptures of the quadriceps tendon, all without medical risk factors, were treated (33 men, 2 women; mean age 55 years). Thirty patients were operated within 14 days after trauma. With an average follow up of 55.4 months (7-168) 29 of 30 still living patients (96.7%) were studied retrospectively. Questionnaire (Lysholm score), physical examination, X-ray of both knees and isokinetic testing were performed. The outcome was significantly (P < 0.001) dependent on the time of operative procedure. Twenty-four patients treated within the first 14 days had 20 excellent and 4 good results, the other 5 one good, 1 satisfying and 3 poor results. Twenty-one of 23 patients (91%) could return to work. The type of repair (direct or transosseous suture with or without augmentation), the kind of postoperative physiotherapy, the age and the body mass index had no influence on the final outcome.

Three-dimensional load measurements in an external fixator.

On the basis of a six-degree-of-freedom adjustable fracture reduction hexapod external fixator, a system which can be used for measuring axial and shear forces as well as torsion and bending moments in the fixator in vivo was developed. In a pilot study on 9 patients (7 fresh fractures and 2 osteotomies of the tibia), the load in the fixator during the healing process was measured after 2, 4, 8 and 12 weeks and at fixator removal. The measured values enabled both the type of fracture to be determined as well as the monitoring of the healing process. In well-reduced type A3 fractures small axial (direction of the bone axis) forces were found in the fixator. A2, B2 and C3 fractures showed distinct axial forces, which decreased during the healing process, according to an increasing load transfer over the bone. Bending moments in the fixator showed good correspondence with the clinical healing process, except in the case of a C3 fracture. A combination of bending moment and axial force proved to be particularly suitable to assess fracture healing. In transverse fractures, the well-known resorption phenomenon of bone in the fracture gap at approximately 4 weeks was detected by the system. Compared with other external fixator load measurements in vivo, the hexapod offers the advantage of being able to measure all forces and moments in the fixator separately and with a relatively simple mechanical arrangement. In our opinion, it will be possible to control fracture healing using this system, thereby minimizing radiation exposure from radiographs. Furthermore, the measurement system is a step towards the development of external fixator systems that enable automatic adjustments of the callus mechanical situation ("automatic dynamization") and inform the patients about the optimal weight bearing of their extremity ("intelligent fixator").

[Experiences in the treatment of midfacial fractures using a fixed-angle osteosynthetic system. Biomechanical results]. / Osteosynthetische Versorgung von Mittelgesichtsfrakturen mit einem multidirektionalen winkelstabilen Plattensystem. Biomechanische Ergebnisse.

AIM: Fixed-angle osteosynthetic systems are characterized by mechanical "locking" of the osteosynthetic screw and plate. These systems have found increasing acceptance and use for osteosynthetic fixation and temporary reconstruction of the mandible. The aim of this study was to investigate the applicability and performance of fixed-angle systems in the treatment of midfacial fractures. MATERIAL AND METHOD: A newly developed fixed-angle osteosynthetic plate system (smart lock) was compared to a conventional system using fresh human skulls. The iatrogenically produced zygomatic fractures of the human skulls were treated by osteosynthesis and biomechanically tested. Furthermore, in a dynamic test series, an artificial bone was subjected to an alternating force of 15 N of up to 1,000,000 cycles. The new screws and plates were subjected to further biomechanical tests. RESULTS: The tests using the fixed-angle implants revealed that an increase of stability of up to 40% can be expected after osteosynthetic fixation. Furthermore, the plates resisted 1,000,000 cycles of alternating forces, whereby the conventional systems failed after 170,000 cycles on the average. CONCLUSION: Fixed-angle systems, due to their construction, provide a high degree of stability even in thin bones of the midface. They appear to be promising for the treatment of midfacial fractures.

Prevention of thromboembolism with low-molecular-weight heparin in orthopedic surgery: a 5-year experience.

A regimen of prophylaxis of thromboembolism with low molecular weight heparin (LMWH) and unfractionated heparin (UFH) in orthopedic surgery is presented. Over a 5-year period, 11,905 patients have been operated in all fields of orthopedic surgery in a big trauma center. In 498 cases, deep vein thrombosis (DVT) was clinically suspected and phlebography was performed: 122 patients had confirmed DVT (rate 0.98%); 59.8% of the DVT were limited to the calf. Nineteen pulmonary embolisms (rate 0.16%) were diagnosed (3 lethal). Heparin-induced thrombocytopenia type II was diagnosed in 12 of 122 patients. Only one of these had received LMWH. The related rates of DVT were highest for tibial head fractures (12.4%), total knee replacement (6.7%), and multiple trauma (6.4%). The extent of DVT was most severe in multiple trauma. The results proved the regimen to be of good clinical use and showed that more attention has to be paid to fractures, especially of the knee; and to patients with multiple injuries.

A hexapod robot external fixator for computer assisted fracture reduction and deformity correction.

Using hexapod robot kinematics, an external fixator adjustable in all six spatial degrees of freedom was developed. As usual with a robot system, bone movements can be accomplished with high precision. Contrary to conventional external fixators any three-dimensional movement is realisable without giving up stability or the necessity to change parts of the construction during the treatment. At first a manually controlled fixator with appropriate software was developed. Then electromotor elements were added, resulting in a "fracture reduction robot" and a fixator featuring load measurement capabilities was built. Finally the concept was extended into an "intelligent fixator" which will accomplish automatically controlled fracture and deformity treatment in the future.

[Theory and software of the hexapod external fixator]. / Theorie und Software des Hexapod Fixateurs externe.

Using hexapod kinematics (Stewart platform), an external fixator was developed that can be adjusted in all six spatial degrees of freedom by means of six linear adjusting elements. With such a system, any desired three-dimensional bone movements, for example, fracture reduction or deformity correction, can be effected exactly, without having temporarily to compromise any stability already achieved or to rearrange the construction during treatment. Since the introduction of the hexapod principle by Stewart in 1965, computerized control has been deemed necessary for its application. This paper describes the mathematical basis and the software developed for clinical use. Mathematical procedures are needed for the calculation of the inverse and forward kinematics of the hexapod, and for the description of three-dimensional movements.

[Corrections using the hexapod]. / Korrekturen mit dem Hexapoden.

The hexapod is a construction that has been subjected to a great deal of investigation in robotics for use in three-dimensional positioning. One use of it is for positioning of the cockpit in flight simulators. Application of the hexapod principle in the external fixator makes it possible to realize prescribed movements of bone fragments with a simple and stable design. The precise setting of the system requires software that has been developed and optimized for clinical use. Translations, axis corrections and rotations are possible individually and also in combinations for correction of complex deformities. The system has advantages, especially in the case of rotations around the longitudinal axis of the bone and in the realization of translation movements. Because the centres of rotation are taken into account by the mathematical calculations, the planning of corrections is simplified. The hexapod system is described, and its clinical application is presented with reference to case reports.

Fracture reduction and deformity correction with the hexapod Ilizarov fixator.

A configuration for the Ilizarov external fixator with six distractors and 12 ball joints in the form of a hexapod was developed. The system allows for six degrees of freedom bone fragment displacement by controlling the distractors. Using this assembly, universal three-dimensional corrections or reductions are possible without the need for complicated joint mechanisms. The device was used in 16 patients: five had displaced tibial fractures with severe soft tissue damage, 10 had deformities or pseudarthroses subsequent to treatment of tibial fractures, and one had an axis deviation in the course of tibial lengthening. Translational (to 40 mm) and rotational deformities (to 33 degrees) were corrected. Final radiographic examinations after the correction procedure was complete showed median residual deformities of 3.5 mm (range, 0-5 mm) and 1 degree (range, 0 degree-4 degrees) in the anteroposterior projection and of 1.5 mm (range, 0-6 mm) and less than 1 degree (range, 0 degree-9 degrees) in the lateral projection. The construction is a useful and important addition to the Ilizarov fixator system. As a bone fixation device it is unique in that its optimal use depends on the availability of computer software.

[Significance of isthmic spondylolisthesis in expert assessment of occupational disease of the lumbar spine]. / Die Bedeutung der isthmischen Spondylolisthesis in der Begutachtung der Berufskrankheit der Lendenwirbelsäule.

In Germany, disc-related disease of the lumbar spine is eligible for workmen's compensation if caused by long-standing work requiring heavy lifting or carrying or extreme trunk-bending (BK 2108). The appraisal of causality is particularly difficult if conditions like isthmic spondylolisthesis preexist. 250 consecutive appraisals in nurses concerning the BK 2108 were analysed, 12 applicants (4.8%) had isthmic spondylolisthesis (4.6% of females and 5.9% of males). The literature about the natural history of isthmic spondylolisthesis is reviewed. A person who has isthmic spondylolisthesis is up to 25% more likely to have significant back trouble during his life than one who does not. Back pain in adults associated with spondylolisthesis is usually heralded by back pain in the late teens or early twenties. Progression of the slip is rarely seen after maturity. Due to the loss of protection by the posterior elements the disc is prone to premature degeneration which, however, does not become clinically apparent in most cases. Longstanding vocational heavy lifting or excessive stooping can negatively influence the natural history of isthmic spondylolisthesis. It can produce symptomatic disease in a person who would otherwise have remained asymptomatic, or it can cause a deterioration in those with preexisting symptoms. Criteria for the appraisal of causality are proposed. It is stressed that the course of the disease in relation to age and vocational strains has to be analysed in each individual case.

[Universal 3-dimensional correction and reposition with the ring fixator using the hexapod configuration]. / Universelle dreidimensionale Korrektur und Reposition mit dem Ringfixateur unter Anwendung der Hexapod-Anordnung.

A new configuration for the Ilisarov fixator with 6 distractors and 12 ball joints in the form of a hexapod is proposed. Using this assembly, a correction or reduction is possible with respect to any given point and axis in space. The primary position of the rings is not critical. The fixator system is statically determined and there is no stress between the longitudinal rods. Difficult corrections like those necessary for rotational deformities can be done without complicated joint mechanisms.

[Standardized ultrasound study with computer-assisted documentation of findings in diagnosis of polytrauma patients]. / Die standardisierte Ultraschalluntersuchung mit computergestützter Befunddokumentation in der Diagnostik des polytraumatisierten Patienten.

Based on the results of a prospective trial to establish the value of routine ultrasound examination in cases of polytrauma or blunt abdominal trauma, we report on our standard ultrasound examination and computer assisted documentation of the findings. Between May 1988 and December 1990 we examined 233 patients with polytrauma or blunt abdominal trauma. The results were compared with those of abdominal lavage (n = 47) performed during the same period. We found a sensitivity of 100% and a specificity of 99.5% for the ultrasound findings and a sensitivity of 80% and a specificity of 100% for the abdominal lavage. We conclude that ultrasonography should be the first diagnostic procedure used in the emergency room in cases of polytrauma and blunt abdominal trauma.